The present application is directed to an apparatus for rapidly freezing tissue specimens, especially potential human cancer tissue at cryogenic temperatures, especially with liquid nitrogen.
Many types of medical procedures surgically remove tissue to test the tissue so as to determine whether or not malignant growth is present. For example, various suspected skin cancers or neoplasms are tested by excising the suspected growth area and then microscopically checking the tissue to determine whether or not cancer is present.
It is also important during such surgical procedures to ensure that all cancerous growth associated with a tumor has been removed. For this purpose the exterior or margins of the excised tissue are studied microscopically to ensure that they are clear of cancerous tissue. The study of the margins requires that the tissue first be hard frozen and then sliced into extremely thin sections. The purpose of the apparatus of the present invention is to prepare specimens for slicing. In particular, the apparatus of the present invention is designed to freeze tissue specimens so that the frozen tissue will have sufficient rigidity in order to be able to be easily sliced and microscopically studied.
The present apparatus represents additional improvements to four previous devices developed by the inventor of the subject of the present application. Applicant's previous patents have included U.S. Pat. Nos. 4,695,339; 4,752,347; 5,628,197 and 5,829,256 which have described various devices and methods for preparing specimens as required for slicing. Certain aspects and procedures which are common to the present application and to one or more of applicant's prior applications and certain of those features which are not new to the present application are not redescribed herein. Consequently, these four previous patents are incorporated herein by reference and should be referred to with reference to further describing certain elements or methods of use of the present invention.
The subject matter of the present application is directed to features which are designed to improve and increase the efficiency and ease of operation of the tissue freezing apparatus and to expand the range of tissue types and size of samples for which it may be employed. In particular, perhaps the most important concern with respect to such a specimen freezing apparatus is that it is always important for the specimens to be frozen as quickly as possible.
There are a number of reasons for expediency, one of the most important of which is that the surgery on the patient must effectively continue until the doctor is convinced that there is no further sign of cancer in the tumor margins. That is, the doctor will initially remove a tissue specimen from the patient that the doctor believes will probably be large enough to contain all of the cancerous tumor.
However, if microscopic study of the margins of the removed tissue demonstrate that cancer has grown outside of the excised tissue, then the doctor must return to the patient and remove a subsequent additional tissue specimen. This subsequent specimen is then tested in the same manner as the first and this process is continued until the specimen proves to be clear of cancerous tissue.
Furthermore, the doctor's time associated with the process is expensive and it is desirable to limit such time. Perhaps one of the more important aspects of the process is that it has been found that relatively fast freezing of the tissue which is referred to as snap freezing produces a much better histologically clean specimen, as compared to slow freezing. The snap freezing reduces crystal formation and provides an overall better specimen to study.
Because of its speed, snap freezing provides rate-controlled freezing in which the speed of heat transfer away from the specimen is more uniform and predictable from one specimen to another. Such high speed heat transfer permits handling of larger individual specimens of all tissues, as well as specimens of tissues which must be sectioned at lower temperatures, such as tissues having a high fat content. Previously, in order to achieve satisfactory microscopic morphology, only smaller specimens of certain tissues such as liver, kidney, fatty tissues and lymph nodes could be handled with conventional slow freezing methods. Consequently, for all these reasons and others, it is highly important to freeze the tissue specimen as quickly as possible.
The apparatus of the present application is specifically designed to improve the quick freezing of the specimen while also providing a number of additional advantages to the process.
One of the problems associated with the prior devices has been that there has been a limitation as to how quickly a physician utilizing the device may process multiple samples. Therefore, it is desirable to be able to process and get ready one set of specimens while another set is in the freezing process. In order to accomplish this the apparatus must include multiple receiving plates which function in cooperation with each other to allow use of the single apparatus with multiple plates. This produces a number of problems since one of the main concerns in processing of the specimen is that the specimen not be rolled sideways on itself during processing steps. Therefore, it is extremely desirable for the opposed plates of the freezing apparatus, once in facing relationship to one another, to move toward each other in a linear fashion as opposed to sliding angularly into each other. An apparatus for accomplishing this process was developed in U.S. Pat. No. 5,628,197 noted above, but this apparatus only functioned in conjunction with a single linear moving plate and a single rotary moving plate. Therefore, it is desirable to develop an apparatus utilizing a single linear moving plate but being able to cooperatively utilize multiple rotary plates that allow preparation actively of some specimens while other specimens are freezing.
The extreme cold associated with cryogenic fluids, especially liquid nitrogen, utilized in conjunction with the apparatus for freezing specimens, produces a number of problems. Obviously, the operator of the apparatus must be quite careful and avoid touching much of the device. Therefore, the operator must take great care in working with the device.
Not only do the cryogenic temperatures present problems to the operator, but also to the apparatus. One of these problems is respect to delivery of the liquid nitrogen to cryogenic discs of the rotary motion platforms. That is, the rotary motion plates of the present apparatus rotate around an axis of approximately 180.degree. and in such rotation the cryogenic fluid supply lines to the disc are likewise rotated. This would not be a problem at room temperature, but the severe cold presents a substantial problem at cryogenic temperatures, since almost all materials which are flexible enough to be rotated at room temperature become fairly rigid at cryogenic temperatures. Consequently, it is difficult to design plastic tubing or the like which can be utilized for this purpose. Rotary quartz couplings have been used in previous embodiments. The quartz couplings function, but tend to be expensive and it is desirable to produce a structure constructed of plastic tubing which will function for this purpose.
It has previously been recognized that quick freezing is an important aspect of the present invention both with respect to speed and quality. However, with respect to speed, it may be as important to be able to heat up the cryodisc to get each of the cryodiscs ready for subsequent specimens.
It is also important for the tissue receiving plates located on the cryodiscs of the linear motion platform to be spaced away from the remainder of the cryodiscs prior to the freezing stage so that the specimen will be more likely to adhere to the plate when it is placed thereon. Consequently, it is desirable to incorporate elements into the apparatus to improve the ability to heat the cryodiscs to near room temperature subsequent to use in freezing a specimen so as to place it in condition for receiving new specimens and to help keep the plate from being chilled prematurely to the placement of the specimen thereon.
It is also desirable within such structures to independently operate at least some of the cryodiscs with respect to others associated with a single platform. That is, for example, in an apparatus having four sets of cryodiscs on each of the linear motion plates and the outer rotary motion plates, it may be desirable to be able to use just two or perhaps only one of those discs depending upon the number of specimens being tested. Consequently, it is desirable to provide the physician with the ability to select all of the discs for use at a time or, when the number of specimens to be tested is less than the number of discs available, to be able to select and quickly freeze a smaller number of the discs.
Another problem associated with prior devices was the difficulty of achieving predictable rate-controlled snap freezing for tissue specimens of all types and sizes, with repeatable results. Certain types of tissue freeze more quickly, whereas other tissues freeze more slowly, with resulting greater incidence of cellular artifacts. Prior devices were more effective at snap freezing smaller tissue specimens. In prior devices the high speed heat transfer required for snap freezing was more difficult to achieve consistently with specimens of larger size. Prior devices were also less effective at snap freezing specimens of tissues having high fat content, which must be sectioned at temperatures as low as about -40.degree. C. to -50.degree. C. Thus, it is desirable to accelerate and enhance rate control of the freezing process in order to avoid formation of intracellular ice crystals, to preserve the microscopic morphology of the tissue and to permit rapid examination of tumor surface margins in all types of tissue and sample sizes. This is accomplished in the apparatus of the present application by prechilling the tissue receiving plates and incorporating structure to distribute a thin layer of frost over the surface of the plates as well as structure to maintain the frost layer until the specimen is placed thereon.